Laser sintering powder, method for producing structure, apparatus for producing structure

ABSTRACT

A laser sintering powder to be sintered by irradiation with a laser light is provided. The sintering powder includes a plurality of metal particles and a binder which binds the metal particles to one another. The binder is sublimated by the irradiation with the laser light. The average particle diameter of the metal particles is 5 μm or more and 10 μm or less, and the average particle diameter of the laser sintering powder is 30 μm or more and 50 μm or less. Further, after a powder layer is formed using the laser sintering powder, this powder layer may be compressed in the thickness direction before or after irradiation with the laser light.

BACKGROUND

1. Technical Field

The present invention relates to a laser sintering powder, a method for producing a structure, and an apparatus for producing a structure.

2. Related Art

A production method for forming a structure by irradiating a metal powder with a laser light is known. This method is suitable for the production of small amounts of various structures because the structure is formed by controlling a laser light using a computer. One such production method is disclosed in JP-T-2001-504897. According to this method, first, a metal powder is spread on a flat plate. Subsequently, a leveling plate is moved along the surface of the metal powder layer to level the metal powder to a given uniform thickness. Subsequently, a protection gas is flowed over the metal powder layer to create a protection gas atmosphere. Subsequently, a laser light is formed into a beam and scanned across the metal powder layer to draw a given image. In a region irradiated with the laser light, the metal powder is sintered and bound.

The steps of spreading the metal powder, leveling the metal powder, and drawing by irradiating the metal powder with the laser light are then repeated as desired. By doing this, the layers of the sintered metal powder are bound to one another, whereby a three-dimensional structure is formed.

Unfortunately, fine metal powder is easily stirred up in the air. Therefore, a metal powder which can be used for laser sintering has an average particle diameter of 30 μm or more. When a plurality of metal powder particles overlap with one another, the metal powder particles on the surface are easily heated by irradiation with the laser light, and the metal powder particles hidden behind the other particles are hardly heated. Due to this, a structure results that includes a completely sintered layer and an incompletely sintered layer stacked on one another in the stacking direction. When the completely sintered layer and the incompletely sintered layer are alternately disposed, the outer appearance of the surface is not glossy. Therefore, it is necessary to polish the surface to achieve the desired glossiness. Thus, although a minute structure can be obtained by laser sintering, the minute structure may have a surface which a polishing tool or a polishing cloth cannot reach, and therefore, it is difficult to make the surface glossy. Therefore, in the production of a structure by irradiating a metal powder with a laser light, a laser sintering powder capable of producing a structure having a glossy surface, a method for producing a structure, and an apparatus for producing a structure have been demanded.

SUMMARY

An advantage of some aspects of the invention is to solve the problem described above, and the invention can be implemented as the following aspects or application examples.

Application Example 1

This application example is directed to a laser sintering powder, which is sintered by irradiation with a laser light, and includes a plurality of metal particles and a binder which binds the metal particles to one another, wherein the binder contains a material which is decomposed and vaporized by the laser light.

According to this application example, the laser sintering powder is configured such that the metal particles are bound to one another by the binder. The size of the metal particles is smaller than that of the laser sintering powder. The laser sintering powder is placed to a given thickness. Then, when the laser sintering powder is irradiated with the laser light, the binder is decomposed and vaporized, and therefore, in the laser sintering powder, the metal particles are separated from one another. The metal particles irradiated with the laser light are heated. At this time, a large energy is applied to the laser sintering powder in a shallow region, and a small energy is applied to the laser sintering powder in a deep region. The heat capacity of the metal particles can be decreased when the size of the metal particles is small as compared with the case where the size of the metal particles is large. Therefore, the temperature of the metal particles can be easily increased. Accordingly, the temperature of the metal particles located in a deep region can be increased, and thus, the metal particles can be reliably sintered even in a deep region.

In the laser sintering, a step of placing the laser sintering powder to a given thickness and a step of drawing with the laser light may be alternately repeated. In the case where the diameter of the metal particles is large and there is a difference in heating of the metal particles by the laser light in the depth direction as in the related art, a laminate in which a completely sintered layer and an incompletely sintered layer are stacked is formed. According to the laser sintering powder of this application example, a difference in heating of the metal particles by the laser light in the depth direction is prevented from occurring. Therefore, a structure formed by irradiating the laser sintering powder with the laser light can be configured such that a surface where the metal particles are stacked has few irregularities. As a result, a structure obtained by laser sintering can be configured to have a glossy surface.

Application Example 2

This application example is directed to the laser sintering powder according to the application example described above, wherein the average particle diameter of the metal particles is 5 μm or more and 10 μm or less, and the average particle diameter of the laser sintering powder is 30 μm or more and 50 μm or less.

According to this application example, the average particle diameter of the laser sintering powder is 30 μm or more and 50 μm or less. When the laser sintering powder is placed to a given thickness and a given pattern is drawn thereon with the laser light, the laser sintering powder having an average particle diameter of 30 μm or more and 50 μm or less is hardly stirred up. Therefore, the laser sintering powder can be irradiated with the laser light in a state where the laser sintering powder is statically stable. Further, since the average particle diameter of the metal particles is 5 μm or more and 10 μm or less, the heat capacity of the metal particles is decreased so that the temperature when heating can be easily increased. As a result, the metal can be sintered to an accurate thickness with good quality, and thus, a structure can be formed with good quality.

Application Example 3

This application example is directed to the laser sintering powder according to the application example described above, wherein the average particle diameter of the laser sintering powder is 3 times or more and 10 times or less larger than the average particle diameter of the metal particles.

According to this application example, the balance of particle diameter between the laser sintering powder and the metal particles is optimized, and thus, both the fluidity of the laser sintering powder and the sinterability of the metal particles can be achieved. Further, when a powder layer formed using the laser sintering powder is compressed in the thickness direction, it becomes easy to moderately crush the laser sintering powder, and also it becomes easy to rearrange the metal particles more densely, and thus, the volume reduction when sintering the metal particles can be further reduced.

Application Example 4

This application example is directed to the laser sintering powder according to the application example described above, wherein the metal particles contain any one of iron, nickel, and cobalt as a principal component and are produced by an atomization method.

According to this application example, the principal component of the metal particles is mainly any of iron, nickel, and cobalt, and therefore, a metal obtained by sintering the laser sintering powder can be any of iron, an iron alloy, nickel, a nickel alloy, cobalt, and a cobalt alloy.

Application Example 5

This application example is directed to the laser sintering powder according to the application example described above, wherein the metal particles contain iron as a principal component, and at least one of nickel, chromium, molybdenum, and carbon.

According to this application example, the principal component of the metal particles is iron, and further at least one of nickel, chromium, molybdenum, and carbon is contained in the metal particles, and therefore, a metal obtained by sintering the laser sintering powder can have corrosion resistance and mechanical rigidity.

Application Example 6

This application example is directed to the laser sintering powder according to the application example described above, wherein the binder is PVA.

According to this application example, the binder is PVA. PVA can bind the metal particles to one another, and therefore, the laser sintering powder can be produced by binding the metal particles to one another by PVA. PVA can be sublimated by the irradiation with the laser, and therefore, the metal obtained by sintering the laser sintering powder can be made not to contain the binder.

Application Example 7

This application example is directed to a laser sintering powder, which is sintered by irradiation with a laser light, and including granulated particles obtained by granulating a plurality of metal particles produced by an atomization method by a spray drying method, wherein the granulated particles have pores therein.

According to this application example, the laser sintering powder includes granulated particles having pores therein. In such granulated particles, the densification of an outer shell portion relatively proceeds, and thus, the granulated particles have a relatively large mechanical strength as compared with particles having no pores therein. Therefore, such granulated particles have excellent fluidity. Further, when a powder layer formed using the laser sintering powder is compressed in the thickness direction, the powder layer is easily crushed, and thus, the powder layer is easily compressed. Accordingly, the laser sintering powder achieves both fluidity and easy compressibility.

Application Example 8

This application example is directed to a method for producing a structure including forming a powder layer composed of a laser sintering powder in which a plurality of metal particles are bound to one another by a binder, and sintering the metal particles by emitting a laser light to the powder layer to draw a given pattern and vaporizing the binder, wherein a structure in which the metal particles are sintered is formed by alternately repeating the forming of a powder layer so as to overlap with the powder layer having the pattern drawn thereon and the sintering.

According to this application example, a powder layer composed of the laser sintering powder is formed. Then, the laser light is emitted to the powder layer, whereby a given pattern is drawn. In a region irradiated with the laser light, the binder is vaporized, and the metal particles are sintered. In the laser sintering powder of this application example, the average particle diameter of the metal particles is smaller than the average particle diameter of the laser sintering powder. The heat capacity of the metal particles is decreased as the size of the metal particles is decreased, and therefore, the metal particles are easily sintered. Accordingly, the temperature of the metal particles located in a deep region of the powder layer can be increased, and thus, the metal particles can be more reliably sintered even in a deep region. Therefore, a structure formed by the method of this application example can be configured such that a surface where the metal particles are stacked has few irregularities. As a result, a structure obtained by laser sintering can be configured to have a glossy surface.

Application Example 9

This application example is directed to the method for producing a structure according to the application example described above, wherein the metal particles irradiated with the laser light are sintered by heating to a temperature at which the metal particles do not melt.

According to this application example, the metal particles are heated to a sintering temperature. If a metal is heated until it melts, the melting metal flows in the direction where the gravitational force or surface tension acts. Therefore, in the case where the metal is heated to a sintering temperature, the metal can be more accurately formed into a shape as it is drawn as compared with the case where the metal is heated until it melts.

Application Example 10

This application example is directed to the method for producing a structure according to the application example described above, wherein the method further includes compressing the powder layer in the thickness direction.

According to this application example, the powder layer is crushed in the thickness direction and consolidated, and therefore, even when the metal particles are sintered, a difference in thickness between the sintered layer and the powder layer can be made sufficiently small. Moreover, when a new powder layer is formed thereon, a powder layer having a uniform thickness can be formed regardless of the condition of the underlayer. Accordingly, even in the case where the volume of the powder layer is greatly reduced accompanying the sintering of the metal particles, the shape of the structure to be produced can be prevented from being largely deviated from the design value, and thus, the dimensional accuracy of the structure can be further enhanced.

Application Example 11

This application example is directed to an apparatus for producing a structure including a powder layer forming unit which forms a powder layer using a laser sintering powder in which a plurality of metal particles are bound to one another by a binder, and a laser light source which emits a laser light to the powder layer.

According to this application example, a powder layer composed of the laser sintering powder is formed. Then, the laser light is emitted to the powder layer, whereby a given pattern is drawn. In a region irradiated with the laser light, the binder is vaporized, and the metal particles are sintered. In the laser sintering powder of this application example, the average particle diameter of the metal particles is smaller than the average particle diameter of the laser sintering powder. The heat capacity of the metal particles is decreased as the size of the metal particles is decreased, and therefore, the metal particles are easily sintered. Accordingly, the temperature of the metal particles located in a deep region of the powder layer can be increased, and thus, the metal particles can be more reliably sintered even in a deep region. Therefore, a structure formed by the apparatus of this application example can be configured such that a surface where the metal particles are stacked has few irregularities. As a result, a structure obtained by laser sintering can be configured to have a glossy surface.

Application Example 12

This application example is directed to the apparatus for producing a structure according to the application example described above, wherein the apparatus further includes a compressing unit which compresses the powder layer in the thickness direction.

According to this application example, the powder layer is crushed in the thickness direction and consolidated, and therefore, even when the metal particles are sintered, a difference in thickness between the sintered layer and the powder layer can be made sufficiently small. Moreover, when a new powder layer is formed thereon, a powder layer having a uniform thickness can be formed regardless of the condition of the underlayer. Accordingly, even in the case where the volume of the powder layer is greatly reduced accompanying the sintering of the metal particles, the shape of the structure to be produced can be prevented from being largely deviated from the design value, and thus, the dimensional accuracy of the structure can be further enhanced.

Application Example 13

This application example is directed to the apparatus for producing a structure according to the application example described above, wherein the compressing unit includes a roller capable of coming in contact with the powder layer.

According to this application example, a possibility that the roller carelessly scrapes off the powder layer is low, and therefore, the powder layer is easily crushed to a desired thickness. Further, the structure of the roller is simple and also small, and therefore, the operation of the apparatus for producing a structure is hardly inhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a schematic perspective view showing the structure of a laser sintering powder.

FIGS. 2A to 2E are schematic views for explaining the sintering of the laser sintering powder.

FIG. 3 is a schematic view showing the structure of a spray drying apparatus for producing the laser sintering powder.

FIG. 4 is a schematic view showing the structure of a laser sintering apparatus to which a first embodiment of an apparatus for producing a structure according to the invention is applied.

FIGS. 5A to 5F are schematic views for explaining a method for forming a structure using a laser sintering powder (a first embodiment of the method for producing a structure according to the invention).

FIGS. 6A to 6D are schematic views for explaining the method for forming a structure using a laser sintering powder (the first embodiment of the method for producing a structure according to the invention).

FIG. 7 is a schematic view showing the structure of a laser sintering apparatus to which a second embodiment and a third embodiment of the apparatus for producing a structure according to the invention are applied.

FIGS. 8A to 8F are schematic views for explaining a method for forming a structure using a laser sintering powder (a second embodiment of the method for producing a structure according to the invention).

FIGS. 9A to 9E are schematic views for explaining the method for forming a structure using a laser sintering powder (the second embodiment of the method for producing a structure according to the invention).

FIGS. 10A to 10F are schematic views for explaining a method for forming a structure using a laser sintering powder (a third embodiment of the method for producing a structure according to the invention).

FIGS. 11A to 11E are schematic views for explaining a method for forming a structure using a laser sintering powder (the third embodiment of the method for producing a structure according to the invention).

FIG. 12 is a table showing an example in which metal particles containing iron, nickel, and chromium were sintered.

FIG. 13 is a table showing examples in which metal particles containing iron, nickel, and chromium were sintered.

FIGS. 14A-E are tables showing examples in which various types of metal particles containing iron as a principal component were sintered.

FIGS. 15A-E are tables showing examples in which various types of metal particles containing iron as a principal component were sintered.

FIGS. 16A-D are tables showing examples in which various types of metal particles containing iron as a principal component were sintered.

FIGS. 17A-D are tables showing examples in which various types of metal particles containing cobalt as a principal component were sintered.

FIGS. 18A-D are tables showing examples in which various types of metal particles containing cobalt as a principal component were sintered.

FIGS. 19A-E are tables showing examples in which various types of metal particles containing nickel as a principal component were sintered.

FIG. 20 is a table showing an example in which metal particles containing nickel as a principal component were sintered.

FIGS. 21A-F are tables showing examples in which metal particles of SUS316L were sintered.

FIGS. 22A-F are tables showing examples in which metal particles of SUS316L were used and sintering was performed by adding a powder layer compressing step which was performed before a laser sintering step (light exposure).

FIG. 23A-F are tables showing examples in which metal particles of SUS316L were used and sintering was performed by adding a powder layer compressing step which was performed after a laser sintering step (light exposure).

FIG. 24A-F are tables showing examples in which metal particles of SUS316L were used, and also a spray drying method or a tumbling granulation method was used as the granulation method, and sintering was performed by adding a powder layer compressing step.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the laser sintering powder, the method for producing a structure, and the apparatus for producing a structure according to the invention will be described in detail based on preferred embodiments shown in the accompanying drawings. That is, in the embodiments, a characteristic laser sintering powder, the production of the laser sintering powder, an example of producing a structure using the laser sintering powder, and an example of an apparatus for producing a structure using the laser sintering powder will be described with reference to FIGS. 1 to 6D. Incidentally, the scales of the respective members in the respective drawings have been appropriately changed so that the respective members have a recognizable size in the respective drawings.

Laser Sintering Powder

First, an embodiment of the laser sintering powder according to the invention will be described with reference to FIG. 1. FIG. 1 is a schematic perspective view showing the structure of the laser sintering powder. As shown in FIG. 1, a laser sintering powder 1 is formed by binding a plurality of metal particles 2.

The average particle diameter (a particle diameter at 50% accumulation in a cumulative particle size distribution on a mass basis) of the metal particles 2 is not particularly limited, but is preferably 5 μm or more and 10 μm or less. As the particle diameter is smaller, the surface roughness of a structure to be produce can be made smaller. However, if the average particle diameter thereof is less than the above lower limit, depending on the constituent material of the metal particles 2, the metal particles 2 are liable to be stirred up in the air, and therefore, it may become difficult to handle the metal particles 2. Further, if the average particle diameter thereof exceeds the above upper limit, depending on the constituent material of the metal particles 2, the sinterability of the metal particles 2 is sometimes deteriorated, and therefore, it may take a longtime to produce a structure. The average particle diameter of a metal powder and the average particle of a granulated powder can be measured by any of a variety of particle diameter measurement methods such as a dynamic light scattering method, a laser diffraction method, a centrifugal sedimentation method, an FFF (Field Flow Fractionation) method, and an electrical sensing zone method.

The constituent material of the metal particles 2 is not particularly limited as long as it is a metal material, but preferably contains a powder produced by an atomization method using any of iron, nickel, and cobalt as a principal component. According to this, the metal obtained by sintering the laser sintering powder 1 can be any of iron, an iron alloy, nickel, a nickel alloy, cobalt, and a cobalt alloy. When the metal particles 2 contain iron as a principal component, the metal particles 2 preferably contain one element or two or more elements in combination selected from nickel, chromium, molybdenum, and carbon. Further, when the metal particles 2 contain nickel as a principal component, the metal particles 2 preferably contain one element or two or more elements in combination selected from chromium, molybdenum, and carbon. According to this, the metal obtained by sintering the laser sintering powder 1 can have corrosion resistance and mechanical rigidity.

Examples of the atomization method include a water atomization method, a gas atomization method, and a spinning water atomization method, and the metal particles 2 may be produced by any method among them.

The shape of the metal particles 2 is not particularly limited, and may be a sphere such as a true sphere or an ellipse, a polyhedron such as a cube or a rectangular parallelepiped, a column such as a circular column or a prismatic column, a conic solid such as a cone or a pyramid, or another irregular shape.

However, as described in detail later, in the case where a step of compressing a powder layer formed using the laser sintering powder 1 in the thickness direction is performed, the aspect ratio of the metal particles 2 is preferably within a predetermined range. Specifically, the average of the aspect ratio of the metal particles 2 defined by S/L wherein S (μm) represents the minor axis of each particle, and L (μm) represents the major axis thereof is preferably 0.3 or more and 0.9 or less, and more preferably 0.4 or more and 0.8 or less. The metal particles 2 having such an aspect ratio have a shape with a certain anisotropy. Therefore, when the metal particles 2 are adhered to one another through a binder 3, the metal particles 2 are easily caught on one another so as to easily exhibit the property of maintaining the adhered state. Then, when a step of compressing a powder layer produced using the laser sintering powder 1 in the thickness direction is performed, a given frictional resistance can be ensured between the metal particles 2, and thus, the compressed powder layer can be prevented from being crushed at once. Accordingly, such a configuration contributes to the shape retainability of the powder layer after compressing.

Here, the “major axis” is the maximum length in the projected image of the metal particle 2, and the “minor axis” is the maximum length in the direction perpendicular to the major axis. Further, the average of the aspect ratio is obtained as an average of the aspect ratio measured for 100 or more metal particles 2.

Further, from the viewpoint of frictional resistance between the metal particles 2, as the atomization method when producing the metal particles 2, a water atomization method or a spinning water atomization method, in which a liquid is used as a medium for atomizing a molten metal, is preferably used. In either of these atomization methods, water is used as the medium for atomizing a molten metal, and therefore, the collision energy when atomizing a molten metal is high, and also the cooling rate when cooling the atomized molten metal is high. Due to this, as compared with a method using a gas as a medium for atomizing a molten metal like a gas atomization method, fine irregularities are more easily formed on the surface of each metal particle 2 to be produced, and thus, the frictional resistance between the metal particles 2 can be relatively increased in this respect.

The surface of each metal particle 2 is covered with the binder 3. The metal particles 2 are adhered to one another by the binder 3. The material of the binder 3 may be any material as long as it is easily vaporized by sublimation or decomposition through heating, and a variety of resin materials can be used. For example, as the material of the binder 3, PVA (polyvinyl alcohol), PVP (polyvinylpyrrolidone) or the like can be used. In this embodiment, for example, PVA is used as the material of the binder 3. The amount of the binder is appropriately adjusted according to the type of the metal particles or the like, but is set to, for example, 0.1 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the metal particles.

In the binder 3, other than the material which is easily vaporized by sublimation or decomposition through heating, a material which is not vaporized may be contained as long as the amount thereof is small so that it does not inhibit the sintering of the metal particles 2. In this case, the amount of the material which is not vaporized is preferably 10% by mass or less, and more preferably 5% by mass or less of the amount of the binder 3.

Further, in the binder 3, multiple types of materials which are easily vaporized by sublimation or decomposition through heating and have sublimation temperatures or decomposition temperatures different from one another may be contained. By incorporating such multiple types of materials, when the binder 3 is heated, the multiple types of materials are sequentially sublimated or decomposed with a given time lag. Due to this, during the process of heating the binder 3, a time for which the binder 3 exists without vaporizing can be secured longer, and thus, a time for which the metal particles 2 are adhered to one another can be ensured longer. As a result, when the powder layer is formed using the laser sintering powder 1 as described below, the shape retainability can be further enhanced, and thus, the dimensional accuracy of a structure to be produced in the end can be further enhanced.

For example, in the case where two types of materials whose sublimation temperatures or decomposition temperatures are different from one another are contained in the binder 3, a difference in sublimation temperature or decomposition temperature is preferably 3° C. or more and 100° C. or less, and more preferably 5° C. or more and 70° C. or less. By setting the difference in sublimation temperature or decomposition temperature within the above range, the shape retainability of the powder layer can be sufficiently enhanced.

The average particle diameter (a particle diameter at 50% accumulation in a cumulative particle size distribution on a mass basis) of the laser sintering powder 1 is not particularly limited, but is preferably 30 μm or more and 50 μm or less, and more preferably 30 μm or more and 40 μm or less. If the average particle diameter of the laser sintering powder 1 is less than the above lower limit, the laser sintering powder 1 is stirred up when it is irradiated with the laser light, and therefore, it becomes difficult to form a structure. If the average particle diameter of the laser sintering powder 1 is larger than the above upper limit, the size of spaces in the laser sintering powder 1 is increased, and therefore, a possibility that air bubbles are formed in the structure is increased.

On the other hand, the average particle diameter of the laser sintering powder 1 is preferably 3 times or more and 10 times or less larger than the average particle diameter of the metal particles 2. By setting the average particle diameter of the laser sintering powder 1 within the above range, the balance of the particle diameter between the laser sintering powder 1 and the metal particles 2 is optimized, and thus, both the fluidity of the laser sintering powder 1 and the sinterability of the metal particles 2 can be achieved. Further, as described in detail below, when a powder layer formed using the laser sintering powder 1 is compressed in the thickness direction, it becomes easy to moderately crush the laser sintering powder 1, and also it becomes easy to rearrange the metal particles more densely, and thus, the volume reduction when sintering the metal particles 2 can be further reduced.

In FIG. 1, in order to make the laser sintering powder 1 easy to understand, three aggregates of the laser sintering powder 1 are illustrated apart from one another. When the laser sintering powder 1 is used, a large number of aggregates of the laser sintering powder 1 are spread out in layers.

FIGS. 2A to 2E are schematic views for explaining the sintering of the laser sintering powder. As shown in FIG. 2A, a large number of aggregates of the laser sintering powder 1 are spread out in layers. In the drawing, the aggregates of the laser sintering powder 1 are arranged in three layers, however, the number of layers of the aggregates of the laser sintering powder 1 to be stacked is not particularly limited. In order to control the arrangement of the metal particles 2 after sintering with good quality, it is preferred to arrange the aggregates of the laser sintering powder 1 in one layer.

As shown in FIG. 2B, subsequently, the laser sintering powder 1 is irradiated with a laser light 4. By the laser light 4, the binder 3 is heated and sublimated. As a result, the binding force between the metal particles 2 by the binder 3 is decreased so that the metal particles 2 easily move. As shown in FIG. 2C, the fluidity of the metal particles 2 is further increased by heating. Then, the metal particles 2 move to occupy the spaces in the laser sintering powder 1. As a result, as shown in FIG. 2D, the metal particles 2 are arranged in lines (layers). The metal particles 2 are heated in a state where the adjacent metal particles 2 come closer to one another, whereby a metal bond is formed. When the irradiation with the laser light 4 is stopped, the metal particles 2 in lines (layers) are cooled. At this time, a metal bond is formed between the metal particles 2, and therefore, a metal block is formed. Then, in the formed structure, the metal particles 2 are densely arranged as shown in FIG. 2E, and therefore, also the side surfaces on the left and right sides in the drawing can be made glossy.

FIG. 3 is a schematic view showing the structure of a spray drying apparatus for producing a laser sintering powder. As shown in FIG. 3, a spray drying apparatus 5 includes a first vessel 6. In the first vessel 6, a disk rotating unit 7, a starting material dropping unit 8, and a hot air blowing unit 9 are provided on a ceiling 6 a. The disk rotating unit 7 includes a motor 10, and a conical rotary plate 11 is attached to a rotating shaft 10 a of the motor 10. The rotary plate 11 is rotated by the motor 10.

The starting material dropping unit 8 includes a second vessel 12. In the second vessel 12, metal particles 2, a binder 3, and a solvent 13 for dissolving the binder 3 are placed. The solvent 13 is not particularly limited and may be any as long as it is a medium which dissolves the binder 3, has a low viscosity, and is readily dried. As the solvent 13, for example, water, methyl alcohol, ethyl alcohol, MEK (methyl ethyl ketone), or the like can be used. In this embodiment, for example, water is used as the solvent 13. The material of the metal particles 2 is prepared in accordance with the composition of a structure to be produced. For example, when the material of the structure is stainless steel SUS301, the material of the metal particles 2 is an alloy containing iron, chromium, and nickel.

The starting material dropping unit 8 includes a motor 14 on the side of the ceiling 6 a, and an impeller 15 is attached to a rotating shaft 14 a of the motor 14. The impeller 15 is rotated by the motor 14. The impeller 15 has a function of stirring the metal particles 2, the binder 3, and the solvent 13. By the impeller 15, the metal particles 2 are uniformly dispersed and the binder 3 is uniformly dissolved in the solvent 13.

An ejection port 16 is disposed on the lower side of the second vessel 12 in the drawing. From the ejection port 16, liquid droplets 17 composed of the metal particles 2, the binder 3, and the solvent 13 are dropped. The ejection port is provided with an electromagnetic valve 16 a. The electromagnetic valve 16 a can adjust the size of the liquid droplets 17 and the ejection frequency.

The hot air blowing unit 9 includes a motor 18 on the side of the ceiling 6 a, and an impeller 21 is attached to a rotating shaft 18 a of the motor 18. The impeller 21 is rotated by the motor 18. A heater 22 is disposed between the motor 18 and the impeller 21. The heater 22 heats the air flowing around heater 22. According to this, the hot air blowing unit 9 causes a hot air 23 to flow downward in the drawing.

The gravitational force acts on the liquid droplets 17 ejected from the ejection port 16. The rotating rotary plate 11 is disposed on the gravitational acceleration direction of the ejection port 16. The liquid droplets 17 hit the rotary plate 11 and break up into small liquid droplets 24. The small liquid droplets 24 move through the air. Around the rotary plate 11, the hot air 23 flows. The solvent 13 in the small liquid droplets 24 is heated by the hot air 23 and released in the air. By doing this, the small liquid droplets 24 are dried and formed into a laser sintering powder 1. The dried laser sintering powder 1 moves downward in the drawing by the gravitational force and is accumulated. According to the procedure described above, the laser sintering powder 1 is produced.

The thus produced laser sintering powder 1 includes many particles (granulated particles) having pores therein. In such particles having pores therein, the densification of an outer shell portion relatively proceeds, and thus, the particles have a relatively large mechanical strength as compared with particles having no pores therein. Therefore, the laser sintering powder 1 including such particles having pores therein has excellent fluidity. Further, since the particles have pores therein, as described in detail below, when a powder layer formed using the laser sintering powder 1 is compressed in the thickness direction, the particles are easily crushed, and thus, the powder layer is easily compressed. Due to this, the powder layer can be more uniformly compressed in the compressing step. Therefore, by incorporating such particles having pores therein, the laser sintering powder 1 can achieve both fluidity and easy compressibility.

In the metal particles 2 having an aspect ratio within the range as described above, a given frictional resistance is ensured between the metal particles 2 as described above, and therefore, an outer shell portion can be rapidly formed during the granulation, and also the densification of the formed outer shell portion easily proceeds. Accordingly, the metal particles 2 having an aspect ratio within the range as described above are useful when forming the particles having pores therein.

The size or the like of the pores contained in the particles is not particularly limited, however, the size thereof is preferably about 1% by volume or more and 50% by volume or less, and more preferably about 5% by volume or more and 30% by volume or less of the laser sintering powder 1. By setting the size of the pores within such a range, the laser sintering powder 1 can particularly achieve both fluidity and easy compressibility. That is, if the size of the pores is less than the above lower limit, the easy compressibility may be deteriorated, and if the size of the pores exceeds the above upper limit, the mechanical strength of the outer shell portion is decreased, and thus, the fluidity may be deteriorated.

The method for producing the laser sintering powder 1 is not limited to the above-described spray drying method, and for example, any of a variety of granulation methods such as a tumbling granulation method, a fluidized bed granulation method, and a tumbling fluidized bed granulation method may be used. However, according to the spray drying method, a laser sintering powder 1 including many (preferably 30% by number or more) particles having pores therein as described above is obtained.

The laser sintering powder 1 may be a mixed powder obtained by mixing an arbitrary powder in the granulated powder produced as described above. The arbitrary powder is not particularly limited in terms of constituent material or mixing amount thereof as long as it does not inhibit the sintering of the metal particles 2.

Apparatus for Producing Structure

Next, a laser sintering apparatus to which a first embodiment of the apparatus for producing a structure according to the invention is applied will be described.

FIG. 4 is a schematic view showing the structure of a laser sintering apparatus to which a first embodiment of the apparatus for producing a structure according to the invention is applied. A laser sintering apparatus 25 includes an XYZ stage 26. The XYZ stage 26 is a device which moves a table 27 in three axial directions perpendicular to one another. Specifically, the XYZ stage 26 includes an XY stage 28 and a lifting device 29. The XY stage 28 moves the table 27 in the horizontal direction. Further, the lifting device 29 is provided on the XY stage 28 and lifts and lowers the table 27. The XY stage 28 includes a biaxial linear motion mechanism, and the lifting device 29 includes a uniaxial linear motion mechanism. According to this, the XYZ stage 26 can move the table 27 in the three axial directions perpendicular to one another.

A bottomed rectangular cylindrical vessel 30 is disposed on the table 27, and the laser sintering powder 1 is spread in the vessel 30. A powder supply device 31 which supplies the laser sintering powder 1 into the vessel 30 is disposed on the upper side of the vessel 30 in the drawing. The powder supply device 31 includes a rail 32 which extends transversely in the drawing. Further, a moving stage 33 which moves along the rail 32 is provided. A hopper 34 which stores the laser sintering powder 1 is mounted on the moving stage 33. The outer appearance of the hopper 34 has a triangular prism shape, and a discharge port 34 a is provided on the side facing a bottom 30 a of the vessel 30.

The discharge port 34 a is provided with an electromagnetic valve 35. The electromagnetic valve 35 opens and closes the discharge port 34 a. When the electromagnetic valve 35 opens the discharge port 34 a, the laser sintering powder 1 flows from the discharge port 34 a to the bottom 30 a of the vessel 30. A leveling plate 36 is attached to the discharge port 34 a. The leveling plate 36 is also called “squeegee”. The electromagnetic valve 35 opens the discharge port 34 a, and the moving stage 33 moves the hopper 34 and the leveling plate 36. By doing this, the laser sintering powder 1 is supplied to the bottom 30 a, and the leveling plate 36 can level the surface of the laser sintering powder 1 flat. A mechanism for moving a cylindrical roller while rotating the roller may be provided in place of the leveling plate 36. Then, by rotating the roller, the surface of the laser sintering powder 1 may be leveled flat. By the moving stage 33, the hopper 34, the leveling plate 36, and the like as described above constitute a powder layer forming unit of the laser sintering apparatus 25.

A laser irradiation unit 37 is disposed on the upper side of the powder supply device 31 in the drawing. The laser irradiation unit 37 includes a laser light source 38. The laser light source 38 may be any as long as it can emit a laser light 4 having a light intensity capable of sintering the metal particles 2, and a laser light source such as a carbon dioxide laser, an argon laser, or a YAG (yttrium aluminum garnet) laser can be used. In this embodiment, for example, as the laser light source 38, a carbon dioxide laser is used.

The laser light 4 emitted from the laser light source 38 is incident on a scanner 41. The scanner 41 includes a mirror 41 a, and the scanner 41 oscillates the mirror 41 a. The laser light 4 incident on the scanner 41 is reflected by the mirror 41 a. Then, the mirror 41 a is oscillated, and thus, the laser light 4 is scanned by the scanner 41.

The laser light 4 reflected by the mirror 41 a is incident on a condensing lens 42. The condensing lens 42 is a cylindrical lens, and condenses the laser light 4 to be scanned on the surface of the laser sintering powder 1. The condensing lens 42 may be a single lens or a combination lens.

A hot air blowing unit 43 is provided on the right side of the laser irradiation unit 37 in the drawing. The hot air blowing unit 43 includes a heater and heats a gas. The hot air blowing unit 43 also includes a motor and an impeller, and the motor rotates the impeller to blow the air. The hot air blowing unit 43 includes an air blowing tube 44 on the side of the vessel 30. The air blowing tube 44 are provided with ejection ports 44 a at equal intervals. The hot air blowing unit 43 sends a hot air 23 to the air blowing tube 44. Then, the hot air 23 is blown on the laser sintering powder 1 from the ejection ports 44 a of the air blowing tube 44.

The laser sintering apparatus 25 includes a control section 45 (e.g., CPU or processor). The control section 45 is electrically or optically connected to the XYZ stage 26, the moving stage 33, the electromagnetic valve 35, the laser light source 38, and the hot air blowing unit 43. The control section 45 controls each member and forms a structure from the laser sintering powder 1.

The laser sintering apparatus 25 includes a chamber 46, and in the chamber 46, the XYZ stage 26, the vessel 30, the powder supply device 31, the laser irradiation unit 37, and the hot air blowing unit 43 are disposed. An inert gas supply section 48 which supplies an inert gas 47 is disposed on the chamber 46. The chamber 46 is filled with the inert gas 47. The type of the inert gas 47 is not particularly limited, however, in this embodiment, for example, argon gas is used as the inert gas 47. That is, the hot air 23 to be blown from the hot air blowing unit 43 is composed of heated argon gas. Further, nitrogen gas may be used as the inert gas 47. According to this, the metal particles 2 can be prevented from oxidizing.

Method for Producing Structure

Next, a first embodiment of the method for producing a structure according to the invention will be described.

FIGS. 5A to 5F and FIGS. 6A to 6D are schematic views for explaining a method for forming a structure using a laser sintering powder (a first embodiment of the method for producing a structure according to the invention), respectively. Hereinafter, with reference to FIGS. 5A to 5F and FIGS. 6A to 6D, the method for forming a structure will be described. In this method, the laser sintering apparatus 25 described above is used.

As shown in FIG. 5A, the laser sintering powder 1 is placed in the hopper 34 of the laser sintering apparatus 25. At this time, the electromagnetic valve 35 is closed to close the discharge port 34 a. By doing this, the laser sintering powder 1 is held in the hopper 34. Then, the distance between the bottom 30 a of the vessel 30 and the leveling plate is set to the average particle diameter of the laser sintering powder 1. Subsequently, as shown in FIG. 5B, the electromagnetic valve 35 is opened to open the discharge port 34 a. By doing this, the laser sintering powder 1 is supplied to the bottom 30 a of the vessel 30 from the discharge port 34 a. The moving stage 33 moves the hopper 34 and the leveling plate 36 while opening the discharge port 34 a. By doing this, the laser sintering powder 1 is supplied to the bottom 30 a. Further, the laser sintering powder 1 is spread on the bottom 30 a of the vessel 30 sequentially, and also the surface of the laser sintering powder 1 is leveled. By doing this, a powder layer 1 a which is the first layer of the laser sintering powder 1 is formed. That is, by the powder layer forming unit constituted by the moving stage 33, the hopper 34, the leveling plate 36, and the like, the first layer of the powder layer 1 a is formed. The thickness of the first layer of the powder layer 1 a may be different from the average particle diameter of the laser sintering powder 1, but is preferably set to the same length as the average particle diameter. By doing this, in the first layer of the powder layer 1 a, the laser sintering powder 1 is spread such that the powder particles do not overlap with one another in the thickness direction. Subsequently, by closing the electromagnetic valve 35 to close the discharge port 34 a, the laser sintering powder 1 is made not to flow out from the discharge port 34 a.

Subsequently, as shown in FIG. 5C, the hot air 23 is blown on the first layer of the powder layer 1 a. By doing this, the first layer of the powder layer 1 a is heated. The temperature of the heated first layer of the powder layer 1 a is lower than the temperature at which the metal particles 2 are sintered. Subsequently, the laser light 4 is irradiated such that the light is condensed on the first layer of the powder layer 1 a. The laser light is scanned by the scanner 41, and also the first layer of the powder layer 1 a is moved in the horizontal direction by the XY stage 28. By doing this, a given pattern is drawn on the first layer of the powder layer 1 a.

The laser sintering powder 1 irradiated with the laser light is sintered at a temperature at which the laser sintering powder 1 does not melt. If the metal is heated until it melts, the melting metal flows in the direction where the gravitational force or surface tension acts. Therefore, the metal is not heated until it melts, but heated to a sintering temperature, whereby a structure of the metal can be accurately formed into a shape as it is drawn.

As a result, as shown in FIG. 5D, a sintered layer 1 b in which the metal particles 2 are sintered is formed in a region of the first layer of the powder layer 1 a irradiated with the laser light 4. Thereafter, by the lifting device 29, the vessel 30 is lowered. Then, the distance between the sintered layer 1 b and the leveling plate 36 is set to the average particle diameter of the laser sintering powder 1.

Subsequently, as shown in FIG. 5E, by the moving stage 33, the hopper 34 and the leveling plate 36 are moved to the left side in the drawing. When the amount of the laser sintering powder 1 in the hopper 34 becomes small, the laser sintering powder 1 is replenished at this time. Then, as shown in FIG. 5F, the electromagnetic valve 35 is opened to open the discharge port 34 a. By doing this, the laser sintering powder 1 is supplied so as to overlap with the first layer of the powder layer 1 a and the sintered layer 1 b from the discharge port 34 a. By the moving stage 33, the hopper 34 and the leveling plate 36 are moved while opening the discharge port 34 a. By doing this, the laser sintering powder 1 is supplied to the bottom 30 a and is spread on the bottom 30 a of the vessel 30 sequentially, and also the surface of the laser sintering powder 1 is leveled. By doing this, a powder layer 1 a which is the second layer of the laser sintering powder 1 is formed so as to overlap with the first layer of the powder layer 1 a and the sintered layer 1 b. Also at this time, the thickness of the second layer of the powder layer 1 a may be different from the average particle diameter of the laser sintering powder 1, but is preferably set to the same length as the average particle diameter. By doing this, in the second layer of the powder layer 1 a, the laser sintering powder 1 is spread such that the powder particles do not overlap with one another in the thickness direction. Subsequently, by closing the electromagnetic valve 35 to close the discharge port 34 a, the laser sintering powder 1 is made not to flow out from the discharge port 34 a.

Subsequently, as shown in FIG. 6A, the hot air 23 is blown on the second layer of the powder layer 1 a. By doing this, the second layer of the powder layer 1 a is heated. Subsequently, the laser light 4 is irradiated such that the light is condensed on the uppermost (second) powder layer 1 a. The laser light 4 is scanned by the scanner 41, and also the second layer of the powder layer 1 a is moved in the horizontal direction by the XY stage 28. By doing this, a given pattern is drawn on the second layer of the powder layer 1 a. As a result, as shown in FIG. 6B, a sintered layer 1 b in which the metal particles 2 are sintered is formed in a region of the second layer of the powder layer 1 a irradiated with the laser light 4. The sintered layer 1 b is formed so as to be connected to the sintered layer 1 b located below. Thereafter, by the lifting device 29, the vessel 30 is lowered. Then, the distance between the sintered layer 1 b and the leveling plate 36 is set to the average particle diameter of the laser sintering powder 1. Also at this time, the distance between the sintered layer 1 b and the leveling plate 36 may be different from the average particle diameter of the laser sintering powder 1.

Thereafter, the step of forming the powder layer 1 a so as to overlap with the sintered layer 1 b formed by drawing and the step of emitting the laser light 4 to the powder layer 1 a are alternately repeated. As a result, as shown in FIG. 6C, in the vessel 30, a structure 49 in which a number of sintered layers 1 b sintered in a given pattern are stacked is formed. Then, as shown in FIG. 6D, the structure 49 is taken out from the vessel 30, and the laser sintering powder 1 adhered to the structure 49 is removed, whereby the production of the structure 49 is completed.

The structure 49 produced using the above production method can be used for various purposes. For example, it can be used as a metal piece to be attached to the teeth for an orthodontic treatment in humans. This metal piece is a component whose variety is wide because it is designed to fit the shape of the teeth to which the metal piece is to be attached. Also in this case, the structure 49 can be produced to fit a required shape.

Further, in addition to this, the structure 49 can be applied to all sorts of constituent parts including: parts for transportation machinery such as parts for automobiles, parts for railcars, parts for ships, and parts for airplanes; parts for electronic devices such as parts for personal computers and parts for mobile phone terminals; and parts for machines such as machine tools and semiconductor production apparatuses.

Second Embodiment

Next, a second embodiment of the method for producing a structure according to the invention will be described.

Hereinafter, a second embodiment will be described, however, in the following description, different points from the first embodiment will be mainly described, and the description of the same matter will be omitted. Further, in the drawings, the same components as in the above-described embodiment will be given the same reference numerals.

FIGS. 8A to 8F and FIGS. 9A to 9E are schematic views for explaining a method for forming a structure using a laser sintering powder (a second embodiment of the method for producing a structure according to the invention), respectively. Hereinafter, with reference to FIGS. 8A to 8F and FIGS. 9A to 9E, the method for forming a structure will be described. In this method, a laser sintering apparatus 25 (a second embodiment of the apparatus for producing a structure according to the invention) shown in FIG. 7 is used.

First, the laser sintering apparatus 25 shown in FIG. 7 will be described. In FIG. 7, in the laser sintering apparatus 25, only a portion around the rail 32 is extracted and shown.

The laser sintering apparatus 25 shown in FIG. 7 is the same as the laser sintering apparatus 25 shown in FIG. 4 except that a compressing unit which compresses the powder layer 1 a in the thickness direction is added.

That is, the laser sintering apparatus 25 shown in FIG. 7 further includes a compressing mechanism (compressing unit) 39, which is disposed on the moving stage 33 that moves along the rail 32, and is capable of coming into contact with the powder layer 1 a and compressing the powder layer 1 a in the thickness direction. When the moving stage 33 moves along the rail 32, the compressing mechanism 39 can move with the movement of the moving stage 33.

The compressing mechanism 39 includes a rotating shaft 391 in parallel with the surface of the powder layer 1 a, a roller 392 rotatably provided around the rotating shaft 391, and a lifting device 393 capable of moving the rotating shaft 391 and the roller 392 in the vertical direction in FIG. 7. There is a low possibility that the roller 392 carelessly scrapes off the powder layer 1 a, and therefore, the powder layer 1 a is easily crushed to a desired thickness. Further, the structure of the roller is simple and also small, and therefore, even if the roller is disposed on the moving stage 33, the driving of the moving stage 33 is hardly inhibited.

In the roller 392, a portion which comes in contact with the powder layer 1 a may be formed from a material which prevents the adhesion to the powder layer 1 a as desired. Further, the portion which comes in contact with the powder layer 1 a may be subjected to a surface treatment with a material which prevents the adhesion to the powder layer 1 a, or an adhesion preventive layer may be deposited thereon as desired.

Further, the compressing mechanism 39 is electrically or optically connected to the control section 45 through a wiring (not shown). According to this, the operation of the compressing mechanism 39 can be controlled by the control section 45.

The structure of the compressing mechanism 39 is not limited to the above-described structure, and for example, in place of the roller 392, an arbitrary member capable of compressing the powder layer 1 a in the thickness direction such as a flat plate which compresses the powder layer 1 a in the thickness direction can be used.

Next, a method for forming a structure shown in FIGS. 8A to 8F and FIGS. 9A to 9E will be described.

First, as shown in FIG. 8A, the laser sintering powder 1 is placed in the hopper 34 of the laser sintering apparatus 25. Subsequently, the laser sintering powder 1 is supplied to the bottom 30 a of the vessel 30 from the discharge port 34 a. As the moving stage 33 moves, the surface of the supplied laser sintering powder 1 is leveled, and therefore, as shown in FIG. 8B, the first layer of the powder layer 1 a having a substantially uniform thickness is formed (a powder layer forming step).

Subsequently, the leveled surface of the first layer of the powder layer 1 a is compressed in the thickness direction by the compressing mechanism 39 (a powder layer compressing step). By doing this, as shown in FIG. 8C, the first layer of the powder layer 1 a is crushed in the thickness direction to reduce the volume, and therefore is consolidated. That is, by moving the roller 392 along the surface of the first layer of the powder layer 1 a while rotating the roller 392, the first layer of the powder layer 1 a is crushed in the thickness direction by the roller 392. At this time, by appropriately adjusting the distance between the bottom 30 a of the vessel 30 and the roller 392 by the lifting device 393, the degree of consolidation can be controlled. A guide to the degree of consolidation can be exemplified as follows: for example, in the case where the sintered layer 1 b is formed by sintering the metal particles 2, the first layer of the powder layer 1 a is consolidated to a thickness equivalent to the thickness of the sintered layer 1 b.

Subsequently, as shown in FIG. 8D, the hot air 23 is blown on the first layer of the powder layer 1 a. By doing this, the first layer of the powder layer 1 a is heated. Subsequently, the laser light 4 is irradiated such that the light is condensed on the first layer of the powder layer 1 a (a laser sintering step). By doing this, a given pattern is drawn on the first layer of the powder layer 1 a. As a result, as shown in FIG. 8E, a sintered layer 1 b in which the metal particles 2 are sintered is formed in a region of the first layer of the powder layer 1 a irradiated with the laser light 4.

Subsequently, as shown in FIG. 8F, a powder layer 1 a which is the second layer of the laser sintering powder 1 is formed so as to overlap with the first layer of the powder layer 1 a and the sintered layer 1 b (a powder layer forming step).

Subsequently, the leveled surface of the second layer of the powder layer 1 a is compressed in the thickness direction by the compressing mechanism 39 (a powder layer compressing step). By doing this, as shown in FIG. 9A, the second layer of the powder layer 1 a is crushed in the thickness direction to reduce the volume, and therefore is consolidated. Also in this case, a guide to the degree of consolidation can be exemplified as follows: when the sintered layer 1 b is formed by sintering the metal particles 2, the second layer of the powder layer 1 a is consolidated to a thickness equivalent to the thickness of the sintered layer 1 b.

Subsequently, as shown in FIG. 9B, the hot air 23 is blown on the second layer of the powder layer 1 a. By doing this, the second layer of the powder layer 1 a is heated. Subsequently, the laser light 4 is irradiated such that the light is condensed on the second layer of the powder layer 1 a (a laser sintering step). By doing this, a given pattern is drawn on the second layer of the powder layer 1 a. As a result, as shown in FIG. 9C, a sintered layer 1 b in which the metal particles 2 are sintered is formed in a region of the second layer of the powder layer 1 a irradiated with the laser light 4.

Thereafter, the step of forming the powder layer 1 a so as to overlap with the sintered layer 1 b formed by drawing, the step of compressing the powder layer 1 a in the thickness direction, and the step of emitting the laser light 4 to the powder layer 1 a are repeated in this order. As a result, as shown in FIG. 9D, in the vessel 30, a structure 49 in which a number of sintered layers 1 b sintered in a given pattern are stacked is formed. Then, as shown in FIG. 9E, the structure 49 is taken out from the vessel 30, and the laser sintering powder 1 adhered to the structure 49 is removed, whereby the production of the structure 49 is completed.

In the structure 49 obtained by the production method as described above, the respective powder layers 1 a are compressed individually, and therefore, when the metal particles 2 are sintered by irradiating the powder layer 1 a with the laser light 4, the volume reduction accompanying the sintering can be minimized.

Specifically, when the metal particles 2 are sintered in a state where the powder layer 1 a is not compressed, depending on the particle diameter of the laser sintering powder 1 or the particle diameter of the metal particles 2, the volume of the powder layer 1 a in the sintered region is relatively greatly reduced accompanying the sintering of the metal particles 2 in some cases. When such a great volume reduction is caused, a large difference in volume between the sintered layer 1 b formed by the sintering of the metal particles 2 and the powder layer 1 a adjacent thereto occurs so that the thickness is different between the sintered layer 1 b and the powder layer 1 a. In such a case, when the step of forming the powder layer 1 a and the step of emitting the laser light 4 are repeated, this thickness difference is accumulated, and therefore, when a new powder layer 1 a is formed, the thickness of the new powder layer 1 a to be formed may vary depending on the condition of the underlayer, that is, whether the underlayer is the powder layer 1 a or the sintered layer 1 b. As a result, the thickness of the new powder layer 1 a becomes non-uniform, and thus, it becomes difficult to produce the structure 49 having a desired shape. Further, when the volume of the powder layer 1 a in the sintered region is relatively greatly reduced accompanying the sintering of the metal particles 2, it may become difficult to irradiate a region hidden behind the powder layer 1 a whose volume is not reduced with the laser light 4.

On the other hand, by adding the step of compressing the powder layer 1 a in the thickness direction as in this embodiment, spaces for causing the volume reduction accompanying the sintering of the metal particles 2 can be crushed in advance. By doing this, even if the metal particles 2 are sintered, the volume reduction accompanying the sintering can be minimized. As a result, a difference in thickness between the sintered layer 1 b and the powder layer 1 a can be made sufficiently small, and therefore, when a new powder layer 1 a is formed thereon, a powder layer 1 a having a uniform thickness can be formed regardless of the condition of the underlayer. Further, the volume reduction accompanying the sintering of the metal particles 2 can be made sufficiently small, and therefore, the inhibition of the irradiation with the laser light 4 by the powder layer 1 a can be prevented.

In this manner, according to this embodiment, even in the case where the volume of the powder layer 1 a is greatly reduced accompanying the sintering of the metal particles 2, the shape of the structure 49 to be produced can be prevented from being largely deviated from the design value, and thus, the dimensional accuracy of the structure 49 can be further enhanced.

Incidentally, also in the second embodiment as described above, the same effects and advantages as those in the first embodiment can be obtained.

Third Embodiment

Next, a third embodiment of the method for producing a structure according to the invention will be described.

Hereinafter, a third embodiment will be described, however, in the following description, different points from the second embodiment will be mainly described, and the description of the same matter will be omitted. Further, in the drawings, the same components as in the above-described embodiments will be given the same reference numerals.

FIGS. 10A to 10F and FIGS. 11A to 11E are schematic views for explaining a method for forming a structure using a laser sintering powder (a third embodiment of the method for producing a structure according to the invention), respectively. Hereinafter, with reference to FIGS. 10A to 10F and FIGS. 11A to 11E, the method for forming a structure will be described. Also in this method, the laser sintering apparatus 25 shown in FIG. 7 is used.

The third embodiment is the same as the second embodiment except that the timing of the step of compressing the powder layer 1 a in the thickness direction is different.

Specifically, first, as shown in FIG. 10A, the laser sintering powder 1 is placed in the hopper 34 of the laser sintering apparatus 25. Subsequently, the laser sintering powder 1 is supplied to the bottom 30 a of the vessel 30 from the discharge port 34 a. As the moving stage 33 moves, the surface of the supplied laser sintering powder 1 is leveled, and therefore, as shown in FIG. 10B, the first layer of the powder layer 1 a having a substantially uniform thickness is formed (a powder layer forming step).

Subsequently, as shown in FIG. 10C, the hot air 23 is blown on the first layer of the powder layer 1 a. By doing this, the first layer of the powder layer 1 a is heated. Subsequently, the laser light 4 is irradiated such that the light is condensed on the first layer of the powder layer 1 a (a laser sintering step). By doing this, a given pattern is drawn on the first layer of the powder layer 1 a. As a result, as shown in FIG. 10D, a sintered layer 1 b in which the metal particles 2 are sintered is formed in a region of the first layer of the powder layer 1 a irradiated with the laser light 4.

Subsequently, the surface of the first layer of the powder layer 1 a is compressed in the thickness direction by the compressing mechanism 39 (a powder layer compressing step). By doing this, as shown in FIG. 10E, the first layer of the powder layer 1 a is crushed in the thickness direction to reduce the volume, and therefore is consolidated. That is, by moving the roller 392 along the surface of the first layer of the powder layer 1 a while rotating the roller 392, the first layer of the powder layer 1 a is crushed in the thickness direction by the roller 392. At this time, in the case where the sintered layer 1 b is present in the moving path of the roller 392, the distance between the bottom 30 a of the vessel 30 and the roller 392 depends on the sintered layer 1 b and cannot be made smaller than the thickness of the sintered layer 1 b. Therefore, the first layer of the powder layer 1 a is consolidated to a thickness equivalent to the thickness of the sintered layer 1 b. Incidentally, also in the case where the sintered layer 1 b is not present in the moving path of the roller 392, when the first layer of the powder layer 1 a is consolidated, it is preferred to consolidate the first layer of the powder layer 1 a to a thickness equivalent to the thickness of the sintered layer 1 b. By doing this, when the second layer of the powder layer 1 a is formed so as to overlap with the first layer of the powder layer 1 a and the sintered layer 1 b, the powder layer 1 a having a uniform thickness is easily formed.

Subsequently, as shown in FIG. 10F, a powder layer 1 a which is the second layer of the laser sintering powder 1 is formed so as to overlap with the first layer of the powder layer 1 a and the sintered layer 1 b (a powder layer forming step).

Subsequently, as shown in FIG. 11A, the hot air 23 is blown on the second layer of the powder layer 1 a. By doing this, the second layer of the powder layer 1 a is heated. Subsequently, the laser light 4 is irradiated such that the light is condensed on the second layer of the powder layer 1 a (a laser sintering step). By doing this, a given pattern is drawn on the second layer of the powder layer 1 a. As a result, as shown in FIG. 11B, a sintered layer 1 b in which the metal particles 2 are sintered is formed in a region of the second layer of the powder layer 1 a irradiated with the laser light 4.

Subsequently, the surface of the second layer of the powder layer 1 a is compressed in the thickness direction by the compressing mechanism 39 (a powder layer compressing step). By doing this, as shown in FIG. 11C, the second layer of the powder layer 1 a is crushed in the thickness direction to reduce the volume, and therefore is consolidated. Also at this time, in the case where the sintered layer 1 b is present in the moving path of the roller 392, the second layer of the powder layer 1 a is consolidated to a thickness equivalent to the thickness of the sintered layer 1 b.

Thereafter, the step of forming the powder layer 1 a so as to overlap with the sintered layer 1 b formed by drawing, the step of emitting the laser light 4 to the powder layer 1 a, and the step of compressing the powder layer 1 a in the thickness direction are repeated in this order. As a result, as shown in FIG. 11D, in the vessel 30, a structure 49 in which a number of sintered layers 1 b sintered in a given pattern are stacked is formed. Then, as shown in FIG. 11E, the structure 49 is taken out from the vessel 30, and the laser sintering powder 1 adhered to the structure 49 is removed, whereby the production of the structure 49 is completed.

In the structure 49 obtained by the production method as described above, the respective powder layers 1 a are compressed individually after the sintered layer 1 b is formed by irradiating the powder layer 1 a with the laser light 4, and therefore, the surface levels of the powder layer 1 a and the sintered layer 1 b are easily equalized. Therefore, when a new powder layer 1 a is formed on the surface of the powder layer 1 a and the sintered layer 1 b, a powder layer 1 a having a uniform thickness can be formed. As a result, a structure 49 having a desired shape can be produced.

Incidentally, also in the third embodiment as described above, the same effects and advantages as those in the first and second embodiments can be obtained.

EXAMPLES

Next, specific examples of the invention will be described.

FIGS. 12 and 13 are tables showing examples in which metal particles of SUS301 were sintered. In FIG. 12, as the metal particles 2, particles of an alloy containing iron, nickel, and chromium were formed and used. The metal particles 2 were produced by a water atomization method. Then, by changing the production conditions, the metal particles 2 having a different average particle diameter were obtained. As the binder, PVA was used, and as the solvent, ion exchanged water was used.

A mixture of the metal particles 2, the binder, and the solvent was placed in the second vessel of the spray drying apparatus shown in FIG. 3. Then, from the ejection port 16, liquid droplets composed of the metal particles 2, the binder, and the solvent were dropped. The liquid droplets were broken up into small liquid droplets by the rotary plate. The small liquid droplets were dried by hot air, whereby a laser sintering powder 1 (granulated powder) was obtained. Then, by changing the size of the liquid droplets and the rotation speed of the rotary plate, various types of laser sintering powders 1 having a different average particle diameter were obtained.

The average particle diameter of the metal particles 2 and the average particle diameter of the laser sintering powder 1 were each obtained as a particle diameter at 50% accumulation in a cumulative particle size distribution on a mass basis using a laser diffraction particle size distribution analyzer (Microtrack HRA9320-X100, manufactured by Nikkiso Co., Ltd.).

In FIG. 13, as shown in Examples 1 to 36, laser sintering powders 1 having an average particle diameter of 25 to 55 μm were formed by performing granulation using the metal particles 2 having an average particle diameter of 3 to 13 In Example 1, a laser sintering powder 1 having an average particle diameter of 30 μm was formed by performing granulation using the metal particles 2 having an average particle diameter of 5.1 Then, the laser sintering powder 1 was sintered, whereby a structure 49 was formed.

As shown in Examples 1 to 15, when the average particle diameter of the metal particles 2 was from 5 to 10 μm, and the average particle diameter of the laser sintering powder 1 was from 30 to 50 μm, the surface of the formed structure was glossy, and good results were obtained.

As shown in Examples 16 to 20, when the average particle diameter of the metal particles 2 was from 5 to 10 μm, and the average particle diameter of the laser sintering powder 1 exceeded 50 μm, the surface of the formed structure was not glossy, and bad results were obtained. As shown in Examples 21 to 25, when the average particle diameter of the metal particles 2 was from 5 to 10 μm, and the average particle diameter of the laser sintering powder 1 was less than 30 μm, the metal particles 2 moved when the laser light 4 was irradiated, and the structures had a poor shape. Accordingly, bad results were obtained under the conditions of Examples 21 to 25.

As shown in Examples 26 to 34, when the average particle diameter of the metal particles 2 exceeded 10 μm, and the average particle diameter of the laser sintering powder 1 was from 30 to 50 μm, the surface of the formed structure was not glossy, and bad results were obtained. As shown in Examples 35 and 36, when the average particle diameter of the metal particles 2 was less than 5 μm, a variation in the particle diameter of the laser sintering powder 1 was large, and a normal laser sintering powder 1 could not be granulated.

FIGS. 14A to 16D are tables showing examples in which various types of metal particles containing iron as a principal component were sintered. In FIGS. 14A to 16D, as shown in Examples 37 to 48, when the average particle diameter of the metal particles 2 was from 5 to 10 μm, and the average particle diameter of the laser sintering powder 1 was from 30 to 50 μm, the surface of the formed structure was glossy, and good results were obtained. As shown in Example 49, when the average particle diameter of the metal particles 2 exceeded 10 μm, and the average particle diameter of the laser sintering powder 1 exceeded 50 μm, the surface of the formed structure was not glossy, and bad results were obtained. In the same manner, as shown in Example 50, even if the average particle diameter of the metal particles 2 was from 5 to 10 μm, when the average particle diameter of the laser sintering powder 1 exceeded 50 μm, the surface of the formed structure was not glossy, and bad results were obtained.

FIGS. 17A-D and 18A-D are tables showing examples in which various types of metal particles containing cobalt as a principal component were sintered. In FIGS. 17A-D and 18A-D, as shown in Examples 51 to 58, when the average particle diameter of the metal particles 2 was from 5 to 10 μm, and the average particle diameter of the laser sintering powder 1 was from 30 to 50 μm, the surface of the formed structure was glossy, and good results were obtained.

FIGS. 19A-E and 20 are tables showing examples in which various types of metal particles containing nickel as a principal component were sintered. In FIGS. 19A-E and 20, as shown in Examples 59 to 64, when the average particle diameter of the metal particles 2 was from 5 to 10 μm, and the average particle diameter of the laser sintering powder 1 was from 30 to 50 μm, the surface of the formed structure was glossy, and good results were obtained.

FIGS. 21A-F are tables showing examples in which metal particles of SUS316L were sintered. In FIGS. 21A-F, as the metal particles 2, particles of an alloy containing iron, nickel, and chromium were formed and used. The metal particles were produced by a water atomization method or a gas atomization method. Then, by changing the production conditions, the metal particles 2 having a different average particle diameter were obtained by a water atomization method and a gas atomization method, respectively. As the binder, PVP was used, and as the solvent, ion exchanged water was used.

In FIGS. 21A-F, as shown in Examples 65 to 70, when the average particle diameter of the laser sintering powder 1 was 3 times or more and 10 times or less larger than the average particle diameter of the metal particles 2, the surface of the formed structure was glossy, and good results were obtained.

Further, it was confirmed that in the case where the metal particles 2 produced by the water atomization method were used, the dimensional accuracy of the formed structure was higher (the deviation from the design value was smaller) as compared with the case where the metal particles 2 produced by the gas atomization method were used. Incidentally, this dimensional accuracy was evaluated by comparing the degree of deviation of the actual value of the height (thickness) of the structure 49 from the design value thereof.

In Examples 65 and 70, when the aspect ratios of the metal particles 2 were compared, the average of the aspect ratio (minor axis S/major axis L) of the metal particles 2 produced by the water atomization method was about 0.54 to 0.75, however, the average of the aspect ratio of the metal particles 2 produced by the gas atomization method was 0.86 to 0.94, which was slightly high.

FIGS. 22A-F are tables showing examples in which metal particles of SUS316L were used and sintering was performed by adding a powder layer compressing step which was performed before a laser sintering step (light exposure). Also in FIGS. 22A-F, the metal particles 2 were produced by a water atomization method or a gas atomization method. Then, by changing the production conditions, the metal particles 2 having a different average particle diameter were obtained by a water atomization method and a gas atomization method, respectively. As the binder, PVP was used, and as the solvent, ion exchanged water was used.

In FIGS. 22A-F, as shown in Examples 71 to 76, it was confirmed that in the case where the metal particles 2 produced by the water atomization method were used, the dimensional accuracy of the formed structure was higher (the deviation from the design value was smaller) as compared with the case where the metal particles 2 produced by the gas atomization method were used.

Further, by comparing FIGS. 21A-F with FIGS. 22A-F, it was confirmed that by providing the powder layer compressing step before the laser sintering step (light exposure), the dimensional accuracy of the produced structure 49 was increased as compared with the case where the powder layer compressing step was not provided.

FIGS. 23A-F are tables showing examples in which metal particles of SUS316L were used and sintering was performed by adding a powder layer compressing step which was performed after a laser sintering step (light exposure). Also in FIGS. 23A-F, the metal particles 2 were produced by a water atomization method or a gas atomization method. Then, by changing the production conditions, the metal particles 2 having a different average particle diameter were obtained by a water atomization method and a gas atomization method, respectively. As the binder, PVP was used, and as the solvent, ion exchanged water was used.

In FIGS. 23A-F, as shown in Examples 77 to 82, it was confirmed that in the case where the metal particles 2 produced by the water atomization method were used, the dimensional accuracy of the formed structure was higher (the deviation from the design value was smaller) as compared with the case where the metal particles 2 produced by the gas atomization method were used.

Further, by comparing FIGS. 21A-F with FIGS. 23A-F, it was also confirmed that in the case where the powder layer compressing step was provided after the laser sintering step (light exposure), the dimensional accuracy of the produced structure 49 was increased as compared with the case where the powder layer compressing step was not provided.

FIGS. 24A-F are tables showing examples in which metal particles of SUS316L were used, and also a spray drying method or a tumbling granulation method was used as the granulation method, and sintering was performed by adding a powder layer compressing step. In FIGS. 24A-F, the metal particles 2 were produced by a water atomization method. Then, by changing the production conditions, the metal particles 2 having a different average particle diameter were obtained. As the binder, PVA was used, and as the solvent, ion exchanged water was used.

In FIGS. 24A-F, as shown in Examples 83 to 88, it was confirmed that when the laser sintering powder 1 produced by a spray drying method was used, the dimensional accuracy of the formed structure was higher as compared with the case where the laser sintering powder 1 produced by a tumbling granulation method was used.

Incidentally, the cross sections of the laser sintering powders 1 produced in Examples 83 to 85 were observed with an electron microscope, and it was confirmed that 50% by number or more of the particles have pores therein. Then, the volume ratio of the pores was calculated for 100 particles among them, and it was about 5 to 50% by volume.

On the other hand, the cross sections of the laser sintering powders 1 produced in Examples 86 to 88 were observed with an electron microscope, and it was found that there were few particles confirmed to have pores therein (20% by number or less).

As described above, according to this embodiment, the following effects are obtained.

(1) According to this embodiment, the laser sintering powder 1 is configured such that a plurality of the metal particles 2 are bound to one another by the binder 3. The laser sintering powder 1 is placed to a given thickness. Then, when the laser sintering powder 1 is irradiated with the laser light 4, the metal particles 2 irradiated with the laser light 4 are heated, and the binder 3 is decomposed and vaporized. At this time, a large energy is applied to a shallow region of the laser sintering powder 1, and a small energy is applied to a deep region thereof. The heat capacity of the metal particles 2 can be decreased when the size of the metal particles 2 is small. Therefore, the temperature of the metal particles 2 can be easily increased. Accordingly, since the temperature of the metal particles 2 located in a deep region can be increased, the metal particles 2 can be reliably sintered even in a deep region.

(2) According to this embodiment, a step of placing the laser sintering powder 1 to a given thickness as the powder layer 1 a and a step of drawing a given pattern with the laser light 4 are alternately repeated. In the case where there is a difference in heating of the metal particles 2 by the laser light 4 in the depth direction, a laminate in which a completely sintered layer and an incompletely sintered layer are stacked is formed. According to the laser sintering powder 1 of this embodiment, since the particle diameter of the metal particles 2 is small, a difference in heating of the metal particles 2 by the laser light 4 in the depth direction is prevented from occurring. As a result, the structure 49 obtained by laser sintering can be configured such that the side surfaces on the left and right sides in the drawing can also be made glossy. Further, the structure 49 formed by irradiating the laser sintering powder 1 with the laser light 4 has a low degree of anisotropy of the strength in the thickness direction. Further, the structure 49 obtained by laser sintering can be configured such that interlayer peeling hardly occurs.

(3) According to this embodiment, the average particle diameter of the laser sintering powder 1 is 30 μm or more and 50 μm or less. When the laser sintering powder is placed to a given thickness and a given pattern is drawn with the laser light 4, the laser sintering powder 1 having an average particle diameter of 30 μm or more and 50 μm or less is hardly stirred up. Therefore, the metal with an accurate thickness can be sintered, and thus, the structure 49 can be accurately formed.

(4) According to this embodiment, the average particle diameter of the metal particles 2 is 5 μm or more and 10 μm or less, and therefore, the heat capacity of the metal particles 2 is decreased so that the temperature when heating can be easily increased. As a result, the metal particles 2 can be sintered with good quality, and therefore, the structure 49 can be formed with good quality.

(5) According to this embodiment, the metal particles 2 are heated to a sintering temperature without melting. If a metal is heated until it melts, the melting metal flows in the direction where the gravitational force acts. By heating the metal not until it melts, but until the sintering temperature is reached, the metal can be accurately formed into a shape as it is drawn. Accordingly, the structure 49 can be accurately shaped.

(6) According to this embodiment, the metal particles 2 are arranged in lines (layers) in the thickness direction. Therefore, the surface roughness of the side surfaces of the structure 49 can be made small.

The present embodiments are not limited to the details described above, and various alterations or improvements can be made by a person with an ordinary skill in the art within the technical ideas of the present invention. Hereinafter some modification examples will be described.

Modification Example 1

In the embodiments described above, the powder layer 1 a is sintered by irradiating the powder layer 1 a with the laser light 4. However, the sintered layer 1 b may be further heated. By doing this, a structure 49 having high peeling resistance strength can be obtained.

Modification Example 2

In the embodiments described above, the structure 49 is formed by stacking the sintered layers 1 b. However, the structure 49 may be further subjected to a heat treatment. This can enhance the performance of the structure 49. In addition, as a post-treatment, a surface treatment may be performed.

Modification Example 3

In the embodiments described above, the scanner 41 scans the laser light 4. However, the XY stage 28 may scan the vessel 30. Then, the scanner 41 is excluded and the mirror 41 a may be fixed. By doing this, the production of the laser sintering apparatus 25 can be facilitated.

Modification Example 4

In the embodiments described above, the laser sintering apparatus 25 is provided with the hot air blowing unit 43. However, when the metal particles 2 can be sintered by the laser light 4 without blowing the hot air 23 on the laser sintering powder 1, the hot air blowing unit 43 may be an air blowing unit which does not include a heating section, or the hot air blowing unit 43 and the air blowing tube 44 may not be provided. According to this, the production of the laser sintering apparatus 25 can be facilitated by decreasing the constituent elements thereof.

Modification Example 5

In the embodiments described above, the powder layer compressing step is performed before or after the laser sintering step, however, the powder layer compressing step may be performed both before and after the laser sintering step. According to this, the dimensional accuracy of the structure 49 to be produced can be further more enhanced.

INCORPORATION BY REFERENCE

The entire disclosures of Japanese Patent Application Nos. 2013-213468 filed Oct. 11, 2013 and 2014-167738 filed Aug. 20, 2014 are expressly incorporated by reference herein. 

What is claimed is:
 1. A laser sintering powder which is sintered by irradiation with a laser light, comprising: a plurality of metal particles; and a binder which binds the metal particles to one another, wherein the binder contains a material which is decomposed and vaporized by the laser light.
 2. The laser sintering powder according to claim 1, wherein an average particle diameter of the metal particles is 5 μm or more and 10 μm or less, and an average particle diameter of the laser sintering powder is 30 μm or more and 50 μm or less.
 3. The laser sintering powder according to claim 1, wherein an average particle diameter of the laser sintering powder is 3 times or more and 10 times or less larger than an average particle diameter of the metal particles.
 4. The laser sintering powder according to claim 1, wherein the metal particles contain any one of iron, nickel, and cobalt as a principal component and are produced by an atomization method.
 5. The laser sintering powder according to claim 4, wherein the metal particles contain iron as a principal component, and at least one of nickel, chromium, molybdenum, and carbon.
 6. The laser sintering powder according to claim 1, wherein the binder is polyvinyl alcohol.
 7. A method for producing a structure, comprising: forming a powder layer composed of a laser sintering powder in which a plurality of metal particles are bound to one another by a binder; and sintering the metal particles by emitting a laser light to the powder layer to draw a given pattern and vaporizing the binder, wherein a structure in which the metal particles are sintered is formed by alternately repeating the forming of a powder layer so as to overlap with the powder layer having the pattern drawn thereon and the sintering.
 8. The method for producing a structure according to claim 7, wherein the metal particles irradiated with the laser light are sintered by heating to a temperature at which the metal particles do not melt.
 9. The method for producing a structure according to claim 7, further comprising compressing the powder layer in a thickness direction.
 10. An apparatus for producing a structure, comprising: a powder layer forming unit which forms a powder layer using a laser sintering powder in which a plurality of metal particles are bound to one another by a binder; and a laser light source which emits a laser light to the powder layer.
 11. The apparatus for producing a structure according to claim 10, further comprising a compressing unit which compresses the powder layer in a thickness direction.
 12. The apparatus for producing a structure according to claim 11, wherein the compressing unit includes a roller selectively coming in contact with the powder layer. 